Many debilitating human diseases are associated with the extracellular misfolding and aggregation of globular proteins to form fibrillar deposits that are rich in ?-sheet. There is considerable evidence that the process is initiated by local unfolding of the native structure to form aggregation-prone amyloidogenic intermediates. Aggregation then proceeds via nucleation-growth or downhill polymerization mechanisms. Despite their key role in amyloidogenesis, influencing the kinetic partitioning between aggregation and refolding pathways, very little is known about the structure of amyloidogenic intermediates because of their strong propensity to aggregate. The goals of the present proposal are to apply state-of-the-art NMR methods to elucidate the fundamental molecular events involved in transthyretin amyloidosis. Transthyretin amyloidosis is associated with numerous neurodegenerative diseases and cardiomyopathies. Misfolding and aggregation of transthyretin leads to fibrous deposits in the peripheral nerves and heart. Deposition of wild type protein is age related, whereas the familial diseases associated with genetic mutations that destabilize the quaternary and/or tertiary structure are early onset. The proposed research will provide novel insights into the fundamental molecular mechanisms by which wild type transthyretin aggregates and by which familial mutations destabilize the native transthyretin tetramer and drive the aggregation cascade. Real-time 19F NMR will be used to map the kinetic aggregation landscape of wild type and pathogenic variant transthyretin, characterize and quantify the population of intermediates that accumulate on the aggregation pathway, and examine mechanisms of inhibition by small molecules and peptides. Multidimensional NMR experiments will be utilized to elucidate the structure and dynamics of an alternate conformational state that promotes tetramer dissociation, and of cytotoxic monomeric and oligomeric intermediates, formed on the aggregation pathway, that promote aggregation and fibril growth. This research will advance our understanding of the underlying molecular events that initiate tetramer dissociation and promote entry into and progression down the aggregation cascade that leads to amyloid formation by both wild type human transthyretin and pathogenic variants.